System for off-mains switching of current consuming devices such as actuators

ABSTRACT

An off mains switching system automatically switches off the mains current to current consuming units and reestablishes operational voltage thereto in response to switching on of such units. A control circuit actuates a voltage coupler in response to a unit becoming switched on and interrupts the voltage supply as a result of a detected termination of noticeable current consumption by such unit. The control circuit includes an operation capacitor with a relatively high capacity to which a charging voltage is supplied as long as the mains are connected. The operating capacitor operates as a voltage source for actuation of a control system in response to restarting of the unit. The control circuit further includes means for internally enabling a connection with the mains for maintaining a voltage supply for the control circuit when the charge on the capacitor drops below a critical level.

BACKGROUND OF THE INVENTION

The present invention relates to an off-mains switching system forautomatically switching off the main voltage to current consumingdevices such as actuators in response to these being switched off.

In different installations, e.g. in connection with an actuatorequipment on adjustable hospital beds, it is, for reasons of security,desirable that the main voltage to the equipment be kept interruptedwhenever there is no actual need for it. Such an interruption oroff-mains switching may be desirable also for other reasons, e.g. foravoiding electrical fields in bedrooms or for saving energy consumptionin devices with idling losses, for example transformers. A superiorinterruption could be arranged by means of a manually operated mainswitch for the single equipment or section of installation, but ofcourse it is to be preferred that the off-mains switching can happenautomatically as a function of an operational switching off of the unit,without any need of remembering to then also operate a main switch.Correspondingly, a detector should be able to react on a new attempt toswitch on the unit, such that the current supply can be reestablished asthe need arises, without a main switch first having to be operated.

At the principal level it is the latter function which is the moreproblematic, because an earlier interruption of the voltage supply willimply that even the said detector is without supply. It is alreadyknown, however, that this problem can be dealt with by the use of abattery in the detector unit, see e.g. DE-A-2624316 and WO 93/11593,such that the voltage available for the detection of a desired restartof the operative unit will be in an acceptable low voltage range.

It is even known that the said battery can be backed up by a condenservoltage, which is maintained as long as the operative unit is subjectedto the mains, and which may remain operative through a relatively longtime after the last switching off of the unit, when a condenser with ahigh discharge resistance is used.

On this background it could be possible to avoid the battery, viz. ifthe equipment is operated daily or even just once a week, as asufficient condenser voltage may well be maintained through some weeksafter each charging. If the equipment is not used for longer time, arenewed start can be arranged by way of current supply from an external,mobile battery, or by actuating the equipment by means of a parallelconnection directly to the mains, using an additional cable and aswitch. For different reasons, however, none of these solutions areparticularly attractive.

SUMMARY OF THE INVENTION

According to the present invention the control system comprises meansfor internally enabling such a coupling to the mains which is requiredfor maintaining the voltage supply of the control system in case of anactuation subsequent to the said condenser being discharged to asubcritical level. Hereby the user will not have to carry out anyspecial actuation acts, if the equipment has been out of use for a longtime, as the required control voltage will be at disposal anyway.

For the practical arrangement, two different types of main principleswill be disclosed. Thus, claim 2 specifies a system, which is inconstant connection with the mains, but noticeably through a voltage andcurrent limiting unit which, in practice, still provides for the desiredoff-mains condition in the user area, but nevertheless is operative torespond to a new attempt of switching on an operation unit of theinstallation system in producing a single actuation of the mainswitching unit, which will then result in a renewed charging of theoperation condenser. Thereafter the latter may be operative for weeks,but the voltage maintained on the auxiliary condenser will ensure thatthe system may be actuated also after the operation condenser havingbeen discharged to below the critical level for actuation of the controlsystem.

The operation condenser acts as a voltage supply for a control circuitwhich, with suitable time intervals, actuates the main switching unitbriefly, just sufficiently to ensure that the operation condenser isrecharged, such that the latter will never get discharged to a pointwhere it cannot fulfil this supply function, as long as the system isconnected with the mains in the first place. The intermittent operationof the control circuit may be based on a clock generator which, with ahigh degree of safety, will effect a recharging of the operationcondenser before it can possibly be subcritically discharged, or on acurrent measurement of the condenser voltage, such that an actuation ofthe main switching unit can be effected whenever the need arises for arecharging of the condenser, for example through relatively few minutesevery several days, all according to the self discharging of thecondenser.

This leads to considerations of such installations which are providedwith a superior off-mains switching system mounted e.g. in a metercabinet. In that kind of systems there will be no usable control orcharging voltage available during the passive periods, and for thatreason it is particularly important that the system of the inventionaccording to claim 3 may provoke a periodic actuation of the mainswitching unit, such that the superior system may thereby detect acurrent consumption that is sufficient to cause a coupling in of themains, whereby in the next stage a recharging of the operation condensercan be effected briefly, i.e. at short duration unless an operation unitin the relevant sub system is actuated so as to condition a longerlasting actuation of the main switching unit and thus an associatedactuation of the superior coupling unit.

Thus, the system according to the invention may be operative duringrelatively long periods of time, measured in days or weeks, without anykind of external voltage supply, and the system will automaticallyorganize the recharging required between these periods.

By the initial start of the system, the same should be made operative bythe required energy charging. In principle it is possible--and known--todo this by connecting a battery, but according to the invention, conferclaim 6, this may be avoided by the use of a detector for initialconnection with the mains. The same detector may then also be active insuch cases where the mains have been superiority disconnected throughsuch a long period that the control equipment has lost its energycharge.

The invention has been developed in connection with an actuatorequipment having DC motors and specific control buttons, whereby thereis used a connection to the mains through a transformer and rectifiersystem. Loads of that type are not well suited as a basis of a detectionof required energy by the switching on of a motor, but on the other handthe control buttons may be used directly as actuator buttons for thecontrol system. However, it will be within the scope of the invention touse for this purpose a load detector , just as in the said superioroff-mains switching systems, such that the system according to theinvention is-not limited for use in connection with any particular typesof operation units.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described in more detail withreference to the drawing, in which:

FIG. 1 is a schematic diagram of a system according to the invention,and

FIG. 2 is a corresponding diagram of a modified and preferred embodimentthereof.

DESCRIPTION OF THE INVENTION

In FIG. 1, numeral 2 denotes a connection to a single phase mains,which, itself, may be provided with an off-mains switching system.Associated wires 4 lead directly to a set of triacs 6 and therefromfurther to an operation equipment with a transformer 8, a rectifier 10and a load 12, which is illustrated as an actuator motor M operable torotate one way or the other by means of relay switches 14 controlled bysolenoids 16, which are actuated by respective operation switches 18,e.g. on a remote control unit.

The triacs 6 are controlled to close and open by means of a photocoupler 20 that is actuated from photo diodes in a control unit 22energized partly from a primary circuit 24, which receives its voltagefrom the unit 10 and is coupled to the operation switches 18, and partlyfrom a secondary circuit 26 that is coupled directly to the mains input2 and includes a rectifier circuit, a voltage limiting diode 28 and anauxiliary condenser 30 diodes 25 are commonly connected at one end at anode between the control unit 22 and the primary circuit 24 and at theother ends separately to the solenoids 16 as shown.

Through the circuit 26,28 the current and voltage on the operationequipment is limited to a minimum, and consequently the auxiliarycondenser 30 is charged relatively slowly. When it has been charged,perhaps after 10-20 seconds, the operation switches 18 can be used foractuation of the motor M, in that they actuate the circuit 22 to switchon the triacs 6 by means of energy from the auxiliary condenser 30,whereby the operational voltage on the equipment 12 is immediatelysupplied via the transformer 8, Hereby there will even be providedcharging current for a large capacitor 32 in connection with the unit24, and thereafter this capacitor will operatively take over the supplyof the unit 22 by the following operations of the system.

The Zeener diode 28 may limit the voltage from the rectifier circuit 26to e.g. 15 V, and the charging current on the auxiliary condenser may bee.g. 8 mA max. When the system is switched off-mains this condenser israpidly discharged, and as mentioned it will be required, for restartingafter a relatively long period of time so that also the capacitor 32 hasbeen discharged, to reestablish the mains connection for initialrecharging of the condenser 30, whereafter the equipment will again beoperative.

The use of the photocoupler 22,20 is advantageous for obtaining aneffective galvanic separation, but the invention is not limited to justthat type of actuation connection.

In the system shown in FIG. 2 the load is shown schematically as a blockB, which comprises a command or detector unit for signalling, through acontrol wire 34, a need for the mains to be switched on, the wire 34leading to a control circuit 36 for producing a light signal to a photocoupler 38 actuating the triac 6, here provided in the phase wire only.Also i FIG. 2, the large operation capacitor is denoted 32. In front ofthe triac 6 a detector circuit 40 is provided, operable to detect theswitching on of the mains or, respectively, the connection of the systemto the mains in the first place, and to actuate the triac 6, preferablyvia a photo coupler, in response to such detection. It will beappreciated that in this system there will be only two electrical wireconnections with the mains and that the capacitor 32 will automaticallybe initially recharged by the actuation of the detector 40. Moreover, itwill be recharged by every switching on of the triac 6.

The control equipment comprises a voltage detector 44 for currentdetection of the voltage on the capacitor 32, which, also here,constitutes the voltage supply for the operative actuations of the triac6 in response to start signals on the wire 34. The capacitor is chargedto a level well above what is required for the actuation of the photocoupler 38, and the detector 44 is designed so as to produce a controlsignal to the trigger circuit 36 whenever the discharging has proceededso far that the remaining charge, with the required safety margin, issufficient for only one more such actuation. In its turn, this willcondition a new and complete recharging, irrespective of the systembeing connected to the mains through a superior off-mains switchingarrangement.

Alternatively, the unit 44 may be a timer, which, without detecting thecapacitor charge, operates to actuate the trigger 36 at such shortintervals that the capacitor will not normally reach a dischargedcondition, e.g. for five minutes every three days.

If a superior off-mains switch has been switched off for a long periodof time it may be necessary, for reestablishing the control voltage onthe capacitor, to switch on a load, e.g. a lamp in the system, or toswitch off and then on of the relevant supply switch for actuation ofthe initial starter circuit.

It should be noted that the principles of the invention are not limitedfor use in connection with the ordinary heavy power system. Admittedly,it is in that area the voltage fields are undesired, but a similaroff-mains arrangement will be relevant even for obtaining a saving ofcurrent consumption, e.g. in connection with transformers with no-loadlosses, confer FIG. 1. In a quite similar manner it will be possible toachieve an energy saving in relevant electronic devices, for example ina control signal detector such as an IR detector, having a receiver unitand an associated identification and control signal producing unit. Thereceiver unit should be constantly operative to respond to an arrivingsignal, but the other units may well be unenergized as long as nosignals are received. Thus, it may be the signal reception itself whichgenerates the trigger signal for a current supply to the other units,including even a supply transformer, and in the meantime the triggervoltage may be held ready in the manner here disclosed, all of coursewith relevant adaptations to the electronic environment, where thecapacitor, then, is again usable for a steady voltage supply of thereceiver unit. It will hardly be relevant to aim at a capacitor time ofthree weeks, but, for example, only of three hours with an associatedbrief recharging time. The system may well be so adapted that it canoperate in connection with a superior off-mains switching arrangement,viz. with quite brief connections of a small load, sufficient to actuatea coupling in of the mains, optionally for few seconds only.

I claim:
 1. An off-mains switching system for automatically switchingoff the mains to current consuming units in response to being switchedoff and for reestablishing operational voltage therefor in response toswitching on of a unit, comprising control equipment for actuation of avoltage coupler in response to a unit becoming switched on and forinterrupting the voltage supply as a result of a detected termination ofa noticeable current consumption by such unit, said control equipmentincluding an operation capacitor with relatively high capacity, to whicha charging voltage is supplied as long as the mains are connected, andwhich, subsequently, operates as a voltage source for actuation of thecontrol equipment in response to a restarting of a unit, wherein thecontrol equipment comprises means for internally enabling a connectionwith the mains, said connection being sufficient for maintaining avoltage supply for the control equipment when the charge on the saidcapacitor drops below a critical level.
 2. A system according to claim1, comprising a current and voltage limiting unit for permanentconnection with the mains the limiting unit comprising a relativelysmall auxiliary condenser, which is kept charged by said limiting unit,and a control circuit for actuating the mains voltage coupler by meansof the voltage of the auxiliary condenser in response to a unit beingswitched on.
 3. A system according to claim 1, wherein the operationcapacitor is connected as a voltage supply for an intermittentlyoperating actuation circuit for the mains voltage coupler in such amanner that said voltage coupler in the absence of an actuation of anoperation unit, is briefly actuated for recharging the operationcapacitor with time intervals sufficiently short to ensure that the saidcapacitor will steadily be charged sufficiently for its activating ofthe actuation circuit.
 4. A system according to claim 3, in which theactuation circuit comprises a timer for activating the mains voltagecoupler at regular intervals.
 5. A system according to claim 3, in whichthe actuation circuit is connected with a measuring circuit and isresponsive to the voltage of the operation for activating the mainsvoltage coupler for recharging of the operation capacitor whenever thevoltage thereof has dropped to a predetermined level, at which theoperation capacitor is able to operate the actuation circuit.
 6. Asystem according to claim 1, in which the control equipment comprisesmeans for detecting the effective connection of the equipment to themains and, in response to such a detection, to actuate the mains voltagecoupler for a period of time, sufficient to effect recharging of theoperation capacitor.
 7. A system according to claim 1, further includingan electronic signal receiver responsive to an incoming signal fordetecting said signal and actuating an external voltage supply, inresponse to the detection said incoming signal.
 8. An off-mainsswitching system for automatically switching off the mains to a currentconsuming unit in response to such unit being switched off and forreestablishing an operational voltage therefor in response to such unitbeing switched on, comprising:a control circuit; a voltage couplerbetween the mains and the unit being responsive to the control circuitfor connecting and interrupting the mains respectively, depending uponthe unit becoming switched on and a termination of current consumptionby the unit, said control circuit including an operation capacitor witha relatively high capacity coupled to the voltage coupler for receivinga charging voltage as long as the mains are connected, and coupled tothe control circuit for acting as a voltage source for actuation thereofin response to a restarting of the unit; and means for internallyestablishing connection of the operation capacitor with the mains formaintaining a voltage supply for the control circuit when said capacitordrops below a selected level whereby the voltage supply to the controlcircuit is maintained at a level sufficient to operate the controlcircuit.